The present invention relates to semiconductor processing equipment and more specifically to a method and apparatus for abatement and optional recovery of by-products from the chemical vapor deposition (CVD) of metal layers, particularly copper layers.
During a typical CVD process, deposition gas or gases inside a processing chamber form a thin film layer on the surface of a substrate being processed. Some CVD processes react two gases together to form the desired layer, such as reacting oxygen with silane to form a layer of silicon oxide. Other CVD processes use a single reactive gas that decomposes to form the desired layer and, typically, byproducts. In addition to the byproducts of the layer-forming reaction, there may be unreacted deposition gas, also known as precursor gas, within the CVD system. Some precursor gases react on surfaces of the CVD system and build up deposits, or decompose to form particles. Similarly, the byproducts of a deposition reaction can build up or form particles. Typically, the CVD system will need to be cleaned at some point, depending on the type and number of deposition processes. This cleaning removes the CVD system from the production stream, and can be very expensive in terms of lost production output.
The semiconductor market is very competitive and semiconductor products have constantly evolved over the last several decades, resulting in smaller and faster microcircuits. Many of the advances in semiconductor processing have focused on making structures, such as metallization lines, on the microcircuits smaller, so that individual devices could be packed closer together, allowing more devices to be fabricated on a single chip.
The most common material for use as a conductor in semiconductor fabrication processes has been aluminum or aluminum alloys. Aluminum is relatively easy to apply, typically by sputtering, and is compatible with both silicon and silicon dioxide. However, as device geometries have gotten smaller, the conductive aluminum traces used on those devices have also gotten smaller. Characteristics of aluminum that did not create significant problems in larger device geometries have become more of a problem as geometries shrank. Specifically, although aluminum is a relatively good conductor, the resistance of very fine aluminum traces can slow down the operation of integrated circuits.
Copper, which has lower resistivity than aluminum, is an alternative metal for use in integrated circuits that has become more economically attractive as devices have become smaller and faster. As with any new technology, unforseen problems arise when the technology is applied to specific products. With copper, new ways of depositing the metal films needed to be developed that would work with existing and planned device geometries. One method that has been developed for depositing a copper film on a substrate uses an organic copper precursor that, under suitable conditions, breaks down to leave a copper film on the substrate. Typically, some of the copper precursor does not react on the substrate, and might react on other parts of the CVD system the substrate is processed in, such as the vacuum pump that is used to exhaust the process chamber. Vacuum pumps produce heat, and the heated pump can cause the unused copper precursor to react on pump surfaces, degrading the pumping efficiency and reliability. Furthermore, the copper-forming reaction of the precursor produces byproducts that may be harmful to personnel or the environment.
Therefore, it is desirable to provide a way of keeping the copper precursor from forming copper on the pump surfaces, and keeping byproducts of the reaction safely contained so that they do not pose a risk to personnel or the environment.
The present invention provides a method and apparatus for removing metal from an exhaust stream of a CVD process. Unreacted metal-film precursor in the exhaust stream is converted on a heated surface of a hot trap to form a volatile metal-organic compound and a metal layer on the surface of the hot trap, thus removing metal from the exhaust stream. In a further embodiment, a metal-organic compound is removed from the exhaust stream by freezing the compound on the walls of a cold trap. The metal recovered in the hot trap and the metal-organic compound recovered in the cold trap may both be recycled, thus reducing the net emissions from the CVD process. The hot trap also protects downstream components, such as a foreline or vacuum pump, from being coated with a metal film or layer of condensed precursor.
These and other embodiments of the present invention, as well as some of its advantages and features are described in more detail in conjunction with the text below and attached figures.